1. Field of the Invention
The invention relates to a lens module comprising at least one exchangeable optical element. In this case, a lens module is understood as meaning part of a projection lens or an illuminating lens for semiconductor lithography or else the entire lens. The invention also relates to a method for flushing a receiving region of an optical element.
2. Description of the Related Art
In the case of high-performance lenses, as is the case for example with projection lenses in semiconductor lithography, imaging errors after an adjustment of the lens and during use of the lens must be minimized. To correct the imaging errors, an optical element that can be exchanged under operating conditions is therefore provided.
In addition, it is advantageous to provide exchangeable optical elements for using the same projection exposure machine to produce different types of semiconductor devices. On account of different structures (for example perpendicular and vertical lines, via holes, honeycomb structures), different semiconductor devices lead to different requirements for the type of exposure in the projection exposure machine, for example with regard to the numerical aperture or the type of illuminating field (for example annular, dipole, quadrupole). Possible means of realizing the desired properties are, for example, filters in or near the pupil plane, which screen spatial regions of the pupil, neutral filters, which have a constant transmission or a transmission that is variable over their surface, or polarizing elements.
In this case, the exchangeable optical elements referred to may be used both in the projection lens and in the illuminating system of a projection exposure machine.
However, there is the risk that freedom from contamination cannot be ensured in the lens module as a result of the fitting and removal of the exchangeable optical element, entailing the introduction of gas from the outside. This introduced gas may have the consequence that the optical elements in the lens module of the projection exposure machine are contaminated by (photo)chemical reaction. Furthermore, the introduced gas may impair the optical properties if it has a refractive index that is different from that of the flushing gas of the lens module.
The present invention is therefore based on the object of providing a lens module, in particular a projection lens for semiconductor lithography, with which no contamination is introduced after an optical element is exchanged and re-fitted, and rapid reuse is made possible.